This study proposes to prospectively investigate the presence of Ureaplasma urealyticum (T-mycoplasmas) in the lungs and fetal membranes of infants dying during the perinatal period. Cultures will also be done for Mycoplasma hominis, Chlamydia trachomatis, cytomegalovirus, aerobic and anaerobic bacteria, including Group B streptococci. The results will be correlated with perinatal death. The two most common disorders in which ureaplasmas have been implicated in the perinatal period are congenital pneumonia and chorioamnionitis. Chlamydia trachomatis and cytomegalovirus have been implicated in infants with interstitial pneumonia. Stillborn and liveborn deaths from 20 weeks' gestation through 28 postnatal days will be studied. It is anticipated that 100 such deaths will occur per year for a total of 300 in the three year period covered by this proposal. The results of cultures will be related to clinical and pathologic findings of the infant and with the histology of the placenta. As controls, 100 placentas of normal, full-term infants will be similarly cultured; 100 additional placentas of infants admitted to the intensive care unit and surviving will also be cultured. The microorganisms studied are sexually transmitted and genitourinary tract infections can occur prior to or during pregnancy. Fetal infection with these microorganisms is a logical sequel. The joint expertise of a pathologist, neonatologist, and microbiologists will all focus on the problem of perinatal mortality. Such a multidisciplinary approach should define the role of the microorganisms studied on poor pregnancy outcome.